Hydrous ruthenium oxide has been attracting attention as an electrode material for the next generation supercapacitors, and there exist a number of reports thereof. For instance, T. R. Jow et al. reported a large capacity (600 to 700 F/g) by nanosizing the hydrous ruthenium oxide particles (diameter: 100 nm) by a sol-gel process (see Non-Patent Document 1).
In addition, Naoi et al. reported that a nano-composite of core-shell type, prepared by coating a proton-conductive polymer on hydrous ruthenium oxide particles, makes high-rate charge and discharge possible, so as to solve a problem that proton diffusion is slow across electrodes of hydrous ruthenium oxide (see Non-Patent Document 2). However, these previous proposals do not sufficiently lead to electrode materials of next generation supercapacitors, thus there are needs for still higher capacity of electrode materials.
On the other hand, it is reported that a sheet electrode, containing highly-dispersed hydrous ruthenium oxide that are supported onto a large surface area carbon, and are dried at a lower temperature under nitrogen gas flow, exhibits a higher capacitance per ruthenium weight and a larger power density per sheet-electrode weight (see Patent Document 1). However, the hydrous ruthenium oxide is likely to dissolve into aqueous electrolytes during the charge and discharge cycles. Furthermore, the documentation describes the capacitance value per weight of ruthenium, but does not describe the capacitance per weight of the material i.e. powder that carries the hydrous ruthenium oxide. However, from the fact that the content of the ruthenium is as low as 3.82% by weight, it is estimated that the capacitance is remarkably lower per weight of the material and far from practical use.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-36441
Non-Patent Document 1: J. Electrochemical. Soc., 142, 2699 (1995)
Non-Patent Document 2: The Chemical Society of Japan, 83rd Annual Spring Conference Proceedings p. 74 (2003)